To deter unauthorized entry to safes time locks have been installed which prevent withdrawal of the locking bolt before expiry of a predetermined time interval. U.S. Pat. Nos. 3,702,451 (Blizard) and 2,140,698 (Goehring) are examples of such devices which ensure that the door cannot be opened except during a permissive time interval following a time delay period which begins with correct setting of the lock tumblers. In neither instance is any special provision included to guard against forcible entry. For the convenient of authorized users of the safe the time period should not be long, but curtailment of the time interval often only delays burglary and does not prevent it.
Various types of combination, or key, lock and gas or dye alarm devices have also been developed with varying degrees of success. In most instances these devices have attempted to thwart forcible entry of a safe by a burglar. A guard against forcible entry has been independently provided according to U.S. Pat. No. 3,500,771 (Fisher et al) where a dye or gas cartridge is activated by a sprung firing pin when an access door of a cabinet or vending machine is forced. An interlock between a lock switch and an alarm device has also been proposed by U.S. Pat. No. 1,743,667 (Gill). In this instance a reservoir of a marking fluid is disposed at the top of the safe which is sprayed on to the safe contents dependent upon two separate controls, viz. the position of the safe door and in response to a time mechanism. Release of the liquid occurs when the door is opened except during the time that the time mechanism operates which commences upon correct operation of a combination lock.
However, the increasing incidence of safe burglary in banks and other staff-attended establishments has led to coercion of the staff in gaining entry to the safe. In most instances for the safety of the staff, they are advised to cooperate if threatened.
It is the principal objection of this invention to provide a security system for a safe which is secure against forcible entry and includes interlocked procedures in sequential operation for permissive access.